I'll add this observation as well: driving all by yourself out on the interstate seems to yield significantly worse mileage, versus driving the same speed in a pack. Perhaps it is the disruption of the wind resistance caused by the cars your are following that makes it easier to get good MPG, as compared to having to plow through the wind resistance all by yourself. I'm not referring to 'drafting', NASCAR-style, rather just following another car or cars at a reasonable distance.

I would think that for a car with a smaller displacement engine, this would have a relatively greater effect than with a more powerful (but more gas-hungry) engine. Of course, it could be that the percentages are the same, but the mileage numbers are magnified because our cars get such good gas mileage (e.g. 44mpg v. 47mpg seems like a lot compared to 18mpg v. 19.3mpg).

 

Also, hills and using the A/C or heater affect the mileage as well. You really do have to learn a new way of driving. As Jason said, you must learn to work with the hybrid instead of against it. Give it a few tanks, watch the instant mileage meter, and note what effects certain driving techniques have on your mileage.